The built-in viewer in windows is fine. I can't really think of a feature that it doesn't have that I need. Could you say why irfanview gets your vote?

It's about speed mostly. And I got used to the shortcuts, ctrl+r to resize, 'i' to check image metadata. I don't really use any of the editing features (I use Paint.NET for edits). In theory I don't need a dedicated image viewer but I like IrfanView so much that I even paid for it so I can have it on company's laptop.

The batch image manipulation features it offers are pretty handy. Plus you can press L or R to rotate an image and it has lossless rotate options as well.

I'm pretty sure it had batch processing capabilities before Photoshop.

> and it has lossless rotate options as well

… and lossless cropping, too.

It's also a paint tool (edit->show paint dialog), and does tricks like swapping channels or repeating the image as a grid of tiles, which are handy when programming something involving raster graphics or textures.

The speed, plugins ecosystem, many more formats supported out of the box, crop being faster and more intuitive, often good enough auto adjust.

Irfan for images and vlc for video is the name of the game for me (and total commander for file management, the efficiency compared to simpler stuff is still in wow territory).

DidectoryOpus is even better, but it's expensive.

IrfanView started so long ago, got and stayed so far ahead.

Wish there was a mac version, but it can be run in an emulator easy enough.

Install it and you'll see within 5-10 minutes the next time you have go through a bunch of images, or do something to a bunch of images.

IrfanView likely still supports more formats, since it was earlier than any other tool. This means any edge cases in file encoding that might not work, or render ideally likely has been solved there first.

It probably has some batch file conversion tricks in it too.

IrfanView also provided for free for a lot of years what was hard to get without paying. If it existed on mac I'd be all over it.

Ah, the windows viewer always wasn't that good.

And if I remember the big first improvement of it was copying a lot of IrfanView.

Since this post, I remembered another old friend that was excellent on windows, AcdSEE. Also worth looking into.

FastPictureViewer